Integration of stimulus history in information conveyed by neurons in
primary auditory cortex in response to tone sequences

S. Klampfl, S. David, P. Yin, S. Shamma, and W. Maass

Abstract:

A critical component of auditory processing is integrating information about
sound features that change over time. Previous studies have shown that the
context of a sound - the immediate history of auditory stimulation - can
have a substantial effect on responses of auditory neurons to a current
sound. In order to characterize these effects, we measured the information
contained in the neural activity in primary auditory cortex (A1) about both
current and preceding sounds. Neural recordings were made from single A1
neurons (n=122) isolated from 23 multi-channel recordings in 4 passively
listening ferrets. The stimulus was a sequence of tones (150 ms duration).
The frequency step between two consecutive tones was always half an octave up
or down. For each neuron, we measured at particular points in time the mutual
information (MI) between its response during a sliding window (20ms) and the
identity of the current and preceding tone. Since direct estimates of MI from
spike trains typically suffer from a systematic error (bias) due to the
limited number of available response trials for a given stimulus, we used a
recently proposed shuffling-based estimator with additional quadratic
extrapolation bias correction (Panzeri et al., 2007). This method produces
reliable information estimates for this particular setup. We found that most
responses (102 out of 122 neurons) contained significant information about
the stimulus throughout the duration of the tone. Of this information, on
average, 60% was about the current tone, while 40% was about the previous
tone. We also trained linear classifiers (Support Vector Machines with linear
kernel) on the low-pass filtered response spike trains of multiple
simultaneously recorded neurons (4-10) to discriminate between the two
possible predecessors for a given tone. The performance the linear classifier
can be viewed as a lower bound on the information contained in the responses
about the previous tone. Performance of up to 80% was achieved. These
results quantify the amount of information contained in the responses of A1
neurons about both currently and previously played tones and demonstrate that
neurons in A1 integrate information about previous input into their current
responses. References: Panzeri et al. (2007), J Neurophysiol, 98(3):1064